Method of exhausting vessels.



U l STTES CHARLES J. THATCHER, 0F UPPER NYACK, NEW YORK.

METHOD OF EXHAUSTING VESSELS.

No Drawing.

To all whom it may concern Be it known that I, CHARLES J. THATCIIER, acitizen of the United States, and a resident of Upper Nyack, in thecounty of Rockland and State of New York, have invented a certain newand useful Method of Exhausting Vessels, of which the following is aspecification.

The process which constitutes this invention relates to the exhaustionof any vessels whatsoever in which it is desirable to rapidly andeconomically attain high vacua. It may be used either for exhaustingelectrical apparatus which are permanently provided with electricalconductors or terminals, such as incandescent lamps, vacuum tubes, etc,or for exhausting nonelectrical apparatus provided with suitableconductors or terminals only for the purpose of exhaustion.

The object of this invention is therefore to attain high vacua in anyvessel requiring completeexhaustion, and the invention consists ineffecting this in a rapid and economical manner without introducing intothe vessel, or otherwise employing, any gas ab sorbing substance.

It is well known that complete exhaustion of vessels to high vacua bymechanical pumping alone is a slow and somewhat costly procedure. Thedifficulty lies in the exhaustion of the last traces of gas.

My invention relates more particularly to the rapid removal of theselast traces of residual gases remaining after mechanical exhaust-ion.

At the present time, so far as I am aware,

the only process of rapid exhaustion is that used in the manufacture ofincandescent lamps and set forth in U. S. Patent #537,693 to ArturoMalignani. Three steps are essential to the operation of this process.They are the preliminary mechanical exhaustion of the lamp to a pressureof about 2 mm. of mercury; the intensive incandescence of the filamentof the lamp in this attenuated atmosphere and at a sufficient intensityto produce a characteristic faint bluish haze throughout the interior ofthe bulb; and lastly, the vaporization of a suitable solid substance,such as arsenic, iodin, sulfur, phosphorus, etc., previously deposit edin some convenient locality Within the interior of the lamp bulb. Theprocess of said patent also comprises additional elespecification ofLetters Patent.

Application filed March 30, 1910. Serial No. 552,310.

Patented J une 4, 1912.

to the three fundamentally essential elements above referred to. Thesetributary steps have been modified in Letters Patent, and in commercialpractice to some degree, as regards the means employed for carrying themout and the sequence of their performance. Otherwise the modern practiceof incandescent lamp exhaustion is substantially identical with thatdevised by Arturo Malignani in 1894 and disclosed in his Letters Patent.In all of these modified procedures as well as in the Malignani processitself, the extraneous solid substance deposited within the lampcombines with and precipitates, when it is vaporized, practically all ofthe gases in the lamp interior, accompanied by the disappearance of theblue haze.

My process, as applied to incandescent lamps, differs from that justconsidered in that I secure a high vacuum without the use of any suchextraneous solid substance. I extend the preliminary mechanical pumpingso that a vacuum is obtained which is generally higher than thatproscribed by Malignani or than that attalncd by mechanical pumping inthe practice of his process. I then institute the intensiveincandescence, proper, of the filament, whereupon a decrease of pressurewhich is equal in extent and rapidity to that produced by the Ma lignaniprocess at once occurs.

.The exhaustion of lamps from 2 mm. down to say 0.2 mm. is thereforeeffected by my process merely by the continuation of mechanical pumpinginstead of by the use of vapors of solid substances as by Malignani. Thecompletion of exhaustion, i. e. from 0.9. mm. down is effected by thesame means in both processes, namely by the intensive incandescence ofthe filament for the same length of time and with the same result, ashas been shown by investigation. ()perating in this manner, the use ofsuitable substances as disclosed by Malignani may be entirely dispensedwith and an equally high vacuum is obtained in substantially the sametime-or even less as I will later show. Since this method of proceduredoes not vary in any manner the degree or duration of the intensiveincandescence'of the filament as now employed in the exhaustion ofincandescent lamps, it is obvious that the filaments will not undergoany changes which do not occur in the process of exments or steps whichI consider tributary haustion now universally employed, and that theyare therefor not injured by the practice of my process.

It has been demonstrated that filaments which are ordinarily used inincandescent lamps have initially a certain ability to precipit-ategases in comparatively high vacuum, but lose this ability after theyhave been incandesced for a period, particularly at voltages above thosethey are designed for. The ability of these filaments to .precipitatethe gases in comparatively high vacua is limited, moreover, asto theamountof gas which they are able to remove. There exists, in otherwords, a certain proportionality between the size of a filament and theamount of gas which it will precipitate; at all events, this is borne.out by the fact that a rapid reduction of pressure to very high vacuaoccurs with certain small and limited quantities of gas at certain lowpressures, but does not with larger quantities at higher pressures. Inview of these considerations it is apparent that the practice of thisprocess in vessels" containing solid conductors requires the use of acon-- ductor or filament which has not previously been lighted for anyappreciable time, particularly at intensive incandescence, andrequiresalso a suitably extended preliminary mechanical exhaustion ofthe vessels. It was the realization of the necessity of these conditionsand the practical application thereof to the exhaustion of vesselswithout the use of extraneous suitable substances which enable me todevise the herein described process. This limited precipitating power ofelectrical conductors may be termed their normal, intrinsicprecipitating power, for it represents that normal quantity of gas whichcan be rapidly removed from a rarefied atmosphere Without any pronouncedor recognizable disruptive effects on the eon-' ductor itself, and--whichremoval is cocasloned by phenomena Which are lntrmsic to anelectrical conductor during the passage of a current. This normal,intrinsic precipltatlng power can be readily ascertained by a fewappropriate trials with any size of the walls of the vessel.

suitably arranged apparatus. By decreasing, step by step, the pressurein the apparatus before the current is first passed through theconductor in each trial, a certain pressure will finally be reached inwhich a decrease of pressure down toa very high.

vacuum occurs with great rapidity. The normal, intrinsic precipitatingpower will always vary, naturally, with the size and nature of theconductor, the intensity of the current passed therethrough, and,apparently, with the nature, condition and In view of these manyfactors, it is impossible to specify the maximum quantity or pressure ofgas which can be exhausted from any certain piece of apparatus, but bymeans of the directions above set out, any one skilled in procedures ofthis nature will readily ascertain the normal, intrinsic precipitatingpower of a conductor during the passage of a current of a suitable highintensity.

In lamps containing carbon filaments it has bee-.1 customary to attachthe filament to the leading-in wires'by means of what.

are technically known as clamps. These latter are composed usually of apaste composition containing carbonaceous materials which decompose whenthe filaments or clamps become red hot, and evolve gas in considerablequantities thereby. For this reason the carbon filaments of the lamphave to be worked as it is termed, either during the final stages ofmechanical exhaustion or immediately thereafter. A very high vacuumcannot be attained or maintained in any incandescent lamp containingsuch or simi-- lar clamps untll these gases have been evolved.

In carrying out the herein described process which constitutes myinvention, with vessels containing solid conductors and clamps of thischaracter, it is obviously necessary,in

order not to destroy the normal, intrinsic precipitating power of thefilament, to effect the working of the clamps without any considerablyextended incandescenee of the filament. I may employ any means to effectthis result, but have found in practice that the carbon filament of anincandescent lamp is still able to precipitate gases at a pressure of0.2 mm., more or less, provided the working of the clamp has beencarefully and rapidly executed. That is, the filament is not injuredfor. the practice of my process providing the clamps are worked by firstturning on the current after the pressure has been reduced to about onemillimeter, or preferably less, by mechanical pumping, and while thesame 'is continuing then increasing the current rapidly to the minimumintensity which will cause the clamps to become red hot in a fewseconds. I maintain the filament and clamps at this degree ofincandescence for a few seconds longer and then immediately shutoffthe'current and continue. the pumping down to the necessary low pressurecorresponding to the normal, intrinsic precipitating power of theconductor. In carrying out this workmg, I must emphasize, it isadvantageous to initiate it at a tolerably low pressure, something lessthan one millimeter, for the clamps then more readily acquire and retaina red heat.

After practically all the gases contained in the filament and clampshave been thus evolved, and thelamp has again been brought down to asuitablelow vacuum by continued pumping, I institute the intensive whichwould obviate the necessity of such' a procedure may be employed incombination with my method of removing gases at low pressures. In lampscontaining filaments and clamps of any description which would notevolveg as'es in any detrimental amount upon the initial incandescenceof the filament this working in the above described manner, or in anyother, may be, of course,

dispensed with. In a somewhat analogous manner, traces of residual gasesmay be removed from vessels by passing a suitable current through thegases themselves by means of terminals. The current must be sufficientlyintense to overcome the resistance of the vacuous space, and to suitablyionize it and produce a pronounced luminous discharge in the vesselpractically until the desired final gaseous pressure is obtained. Inthis modification, also, the amount or mass of residual gas within thelamp should not exceed the normal, intrin-:

sic precipitating power of the electrically excited conductor, whichvalue may be ascertained for any type of vessel by a few appropriatetrials as before explained.

A treatment similar to the working before referred to may be carried outin vessels containing gaseous conductors, provided it is renderednecessary by the presence of substances, on or near the terminals or inother interior portions of the vessel, which might evolve gases eitherduring the process of exhaustion or in actual use. Any vessel, indeed,exhausted by my process,

should be previously heated by some suit able means sufficiently todrive off from the interior walls the films of water or gas whichnormally adhere to the surfaces of solids. After either or both of thesetreatments have been efiected and the gas or vapor thus evolved has beenpumped out until a suitable pressure corresponding to the normal,intrinsic precipitating power of the conductor has been reached, theprocess of exhaustion is completed by passing a current of suitableintensity through the vessel as before explained, and preferably afterthe pump has been shut ofi My process can of course be carried out byother means and in other Ways than those specifically described. Forexample, the exhaustion of incandescent lamps can be effected bythepassage of a suitable current, not through the filament of the lampitself but through a supplementary solid. conductor or even through theresidual gases of the lamp, after the filament has been worked as beforeexplained if necessary, and after the lamp has been exhaustedby pumpingor other means to a pressure corresponding to the normal, intrinsicprecipitating power of the conductor used for this purpose. TlllSprocedure would bepreferable in lamps containing very sensitivefilaments, which would be damaged by even a brief period of intensiveincandescence, and in low voltage lamps. My process may, indeed, be thuscarried out with lamps of any description whatsoever, in which it isthought that the filament is unsuitable, or might" be injured byreliance upon it, to eflect exhaustion as herein set forth. Suchaprocedure entirely dispenses with even the period of intensiveincandescence of the filament now employed in the exhaustion ofincandescent lamps and obviates any damaging effects to the filamentarising therefrom. One method of safeguarding the filament in this waywould be to eifect the exhaustion by the passage of a current throughthe gases of the lamp by means of suitably applied external terminals orauxiliary internal terminals.

It will of course be understood that I do not confine myself to thespecifically described methods of passing electrical currents throughexhausted vessels or suitably ionizing or electrically exciting thegases in their interior.

By exhausting vessels according to the herein described process certainpractical and important advantages result. Thus it -is economical todispense with the use of a suitable gas-absorbing substance inexhausting incandescent lamps. Although the process of exhaustion nowemployed requires the use of a very small amount of a suitable substancesuch as phosphorus, the total cost of the same and of its depositionin'the tubultures of large numbe'fs of lamps is considerable. By myprocess the tubulture can be made shorter. The consequent saving inglass tubing amounts to a further considerable item.

Incandescent lamp exhaustion by my process is also more economical thanthe present practice in that it requires less attention on the part ofthe lamp operator and is, In reality, more rapid. A comparatlvely largenumber of lamps can be attached to each pump and the mechanicalexhaustion can then proceed while the operator is attaching or attendingto another S8I'1E.S 0f lamps. After the properyacuum hasbee'n reached,as ascertained if desirable by a readlng of the gaseous pressure bymeans of a suitable gage attached to each series of lamps, the currentcan then be'turned on 1n all of the lamps simultaneously and continueduntil the exhaustion is completed. A determination of the pressurecommon to all the lamps can now be made again and in a very few secondsby the said gage, to insure that the requisite high vacuum has beenattained; or the disappearance of the blue haze may be relied upontodetermine this point. By a suitable arrangement of gas jets the lampsmaythen be all sealed of]? simultaneously and the current finally turned011'. With a fairly good pump, a vacuum of 0.2 mm. or less can beattained in considerably less than 2 minutes as contrasted with the 30to 60 seconds of mechanical exhaustion now employed in the operation ofthe Malignani process. But even allowing as much as 5 minutes formechanical exhaustion, during which time the operators attention can begiven to another series of lamps, the exhaustion of a bank of twentyorlmore lamps by my process will not occupy ten minutes altoget-her, orless than -1- minute per lamp.

This method of'procedure, rapidity of cx-.

haustion and output per operator cannot be duplicated, by the presentpractice of lamp exhaustion, as each lamp requires individualattentionand treatment on the part of the operator during the critical portion ofthe exhaustion. In addition to these advantages the hereindescribedprocess is superior to that now in use in that it more per: fectlyinsures the continuance of a high vacuum in the lamp during actual use.The

gases are precipitated by my process in a more stable and permanentcombination than by the present practice. The substance, phosphorus,which is now used, and which hold the gas in physical combination as Ihave demonstrated, is vaporized in the lamp bulb at comparatively lowtemperatures. The temperature which will produce this eflect is easilyreached during actual use of the lamp, and upon vaporization of thephosphorus it liberatessome or all of the gas with which it is combined.The condltlons under which the combination of the residual gases withphosphorus originally occurred are not duplicated in actual use. Thisliberation of gas and impairment of the vacuum, when once started, iscumulative and results in a considerable reductlon in the useful life ofthe lamp. This effect cannot occur when my process is used, for thegases are precipitated and pennanently held in combination withpractically non-vaporizing particles such as carbon, tungsten or thelike.

I claim 1. The process of rapidly producing high precipitate theresidual vacua in vessels, which consists in subjecting them to asuitable preliminary mechanivacua in'ineandescent lamps, whichconsistsin subjecting them to a suitable preliminary mechanicalexhaustion and passing a sultable electric current through the lamps to3 gases and complete the exhaustion. 3. The process of rapidly producinghigh vacuain incandescent lamps, which consists in subjecting them to asuitable preliminary mechanical exhaustion, and then bringing thefilaments to intensive incandescence to complete the exhaustion.

4. The process of rapidly producing high vacua in incandescent lamps,which consists in subjecting them to a suitable preliminary mechanicalexhaustion and then bringing the-filaments to intensive incandcscence toprecipitate the residual gases andcomplete the exhaustion.

5. The process of rapidly producing high "acua in'vessels containing anelectrical conductor, which consists in mechanically exhausting themuntil the mass of gas within the vessels does not exceed the normal,intrinsic,precipitatingpower of the conductor, and then passing a suitabe electric current through the conductor to precipitate the residualgases and complete the exhaustion.

6. The process of rapidly pr ducing high vacua in incandescent lamps,which consists in mechanically exhausting them until the mass of gaswithin the lamps doesnot exceed the normal intrinsic, precipitatingpower of the filaments, and then bringing the filaments to intensiveincandescence to complete the exhaustion.

'7. The process of rapidly producing high vacua in incandescentla1nps,which consists in mechanically exhausting the same to a pressurenot exceeding two-tenths of a millimeter of mercury, and then bringingthe filaments to intensive incandescence to com-.

plete the exhaustion.

Signed at New York, in the county. of

CHARLES J. THATCHER.

Witnesses:

LAURA E. SMITH, FREDK. F. SCHUETZ.

